1. Field of the Invention
The present invention relates generally to capacitors and, more particularly, to flexible multilayer thin film capacitors for applications in specialized shapes.
2. Description of the Related Art
Capacitors are generally fabricated in conventional physical shapes and sizes dictated by the capacitor materials, the manufacturing process, the end use, and the desired electrical properties. Ceramic or thin film multilayer capacitors, for example, can be in the form of chips, whereas other multilayer film capacitors can be in the form of encapsulated rolls. Electrolytic capacitors can be in the form of rolls housed in metal containers. These shapes and packages have wide applications for positioning on or near circuit boards. In a number of other applications, however, space is at a premium and the capacitor shape, in addition to the size, is a critical factor determining the overall size and shape of the electrical assembly.
Several in situ deposited capacitor fabrication techniques that involve the formation of large strips of capacitor elements on a drum or on a long strip or web transported over rolls can be used to form selected capacitor geometries. These capacitor strips have conventionally been subdivided into chip forms for providing mass markets with common capacitor sizes and shapes. One example of this is the polymer monolithic capacitor (PML) fabrication process developed by General Electric Company and performed on a drum in a vacuum chamber, as described in Angelo Yializis et al., "A New High Temperature Multilayer Capacitor with Acrylate Dielectrics," IEEE Transactions on Components, Hybrids, and Manufacturing Technology, Vol. 13, No. 4, 611, December 1990. Employees of Siemens Aktiengesellschaft have described a glow discharge polymerization process for providing dielectric layers which are alternated with vapor deposited metal layers on a drum rotating through vacuum chambers in which the individual deposition processes are performed in Behn, U.S. Pat. No. 4,378,382, Mar. 29, 1983. Another multilayer capacitor fabrication technique is described in J. L. Davidson et al., "Multilevel DLC (Diamondlike Carbon) capacitor structure," SPIE Vol. 871 Space Structures, Power, and Power Conditioning 308 (1988). There is no indication that the capacitors in these fabrication techniques are formed into any shapes other than chips.
Some technologies are capable of making capacitors more compact than electrolytic capacitors while providing beneficial thermal and electrical characteristics. For example, as disclosed in commonly assigned Fisher et al., "Low-Profile Capacitor and Low-Profile Integrated Capacitor/Heatspreader," application Ser. No. 08/214,508, filed Mar. 18, 1994, an amorphous hydrogenated carbon dielectric material, frequently referred to as "diamond-like carbon" (DLC), has been used at General Electric Company's Research and Development Center to fabricate multilayer chip capacitors which have a potential for having higher energy storage density than capacitors normally available due to the high dielectric strength of the DLC which permits the use of very thin films. However, for capacitance values in the range of 1 microfarad and higher, hundreds and even thousands of layers of dielectric and metal can be required because the dielectric constant of the DLC dielectric material has a range of three to five. Additionally, as the voltage requirement for a capacitor used in a particular application increases, there is a need for greater thickness of the dielectric material, leading to a requirement for an even higher numbers of layers. The high number of layers can increase cost and complexity of fabrication processes, and mechanical stresses which can be created within the capacitor can cause deformations or delaminations.